In recent years, a CRT display as an image display device has been gradually replaced by a flat panel display (FPD), which is lighter and thinner than the CRT display, such as a liquid crystal display (LCD), a plasma display panel (PDP), a field emission display (FED), or an organic light-emitting diode (OLED) display. Further lightening of any such FPD is being promoted, and hence there arises a need for further thinning a glass substrate corresponding to one of the main components of the FPD.
Further, for example, there is a growing use of an organic light-emitting diode not only for applications to a display that uses TFTs to blink light of three primary colors, but also as a plane light source, such as a backlight of the LCD and a light source for interior illumination, which emits only monochrome (for example, white) light. An illumination device that uses the organic light-emitting diode as alight source may have a freely deformable light-emitting surface as long as the organic light-emitting diode is constructed of a flexible glass substrate. Therefore, from the viewpoint of ensuring sufficient flexibility, there is also promoted further thinning of the glass substrate (forming of the glass substrate as a glass film) to be used for this type of illumination device.
As a manufacturing method for a glass film (sheet glass), for example, there is a method disclosed in Patent Literature 1 described below. Specifically, by a so-called downdraw method, a glass base material is drawn downward vertically to form a glass film ribbon, and the glass film ribbon is transported toward a downstream side while being curved in a longitudinal direction of the glass film ribbon to convert a traveling direction of the glass film ribbon from a vertical direction to a horizontal direction. After that, the glass film ribbon is subjected to a widthwise cutting process to obtain a sheet glass having a predetermined dimension. Note that, depending on the thickness of the glass film ribbon, after the traveling direction is converted into the horizontal direction, the glass film ribbon may be rolled around a roll core without performing the widthwise cutting process, to thereby obtain a so-called glass roll.